Download Gas Hydrates: Our Energy (and Climate) Future?

Gas Hydrates: Our Energy (and Climate) Future?
Lecture Outline:
1)What are gas hydrates anyway?
2)Gas hydrates as an energy source – pros
and cons
3)Gas hydrates and climate change: adding
fuel to the flames?
Hydrates - What are they?
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
Gas Hydrates are solids formed
from hydrocarbon gas and liquid water

They resemble wet snow and can
exist at temperatures above the
freezing point of water

They belong to a form of
complexes known as clathrates
Clathrates - What are they?

Clathrates are substances having a lattice-like
structure or appearance in which molecules of
one substance are completely enclosed within
the crystal structure of another

Hydrates consist of host molecules (water)
forming a lattice structure acting like a cage, to
entrap guest molecules (gas)
 CH4 (most common), CO2, H2S form hydrates
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98% in ocean
2% on land
white dot = gas samples recovered
black dot = hydrate inferred from seismic imaging
dotted lines = hydrate-containing permafrost
http://walrus.wr.usgs.gov/globalhydrate/images/browse.jpg
using seismic-reflection profiles
Bottom Simulating Reflection (BSRs)
http://woodshole.er.usgs.gov/project-pages/hydrates/hydrate.htm
Methane Hydrate stability diagram
-methane hydrates can occur at
water temperatures up to 30°C,
if the pressure is high enough
-stable over most of ocean floor!
a methane hydrate lattice
redrawn after Kvenvolden (1993)
“The Burning
Snowball”
Methane hydrate
supporting its own
combustion
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Methane Hydrates as an energy source
BENEFITS:
- 1 cubic meter of gas hydrate (90% site occupied) = 163 m3 of gas
-there is A LOT of it,
and it’s everywhere
-clean-burning
natural gas
• USA has gas hydrate reserves of 112,000-676,000 trillion cubic
feet (tcf)
• USA has 2,200 tcf of natural gas reserves (EIA)
• USA uses 25-30 tcf/yr of natural gas
• India and Japan are leading the charge to hydrate recovery
An Energy Coup for Japan: ‘Flammable Ice’
Water depth: 1000m
subfloor depth: 300m
NYTimes, 3/12/13
Methane Hydrates as an energy source
PROBLEMS:
-hydrate dissociation upon recovery; engineering challenge
-expense of long pipelines across continental slope, subject
to blockage with solid hydrate
-methane release into atmosphere problem for climate change
(20x more potent than CO2)
-fragile ecosystems surround
sediment surface hydrates
& seeps
ice worm that lives in hydrate
photo by Ian Mc Donald
1 cubic meter of gas hydrate (90% site occupied) = 163 m3 of gas + .87 m3
Undersea slides (slope failures) may be caused by methane hydrate dissociation;
implications for pipeline?
Large, expensive pilot programs
focus on drilling in frozen
permafrost areas
Ex: Mallik, Canada
http://energy.usgs.gov/other/gashydrates/mallik.html
New ocean sediment drilling technologies
invented for hydrate recovery and storage
an Ocean Drilling Program core locker
with lone hydrate core in pressurized chamber
dissociating methane hydrate at sediment/water interface
Westbrook et al., 2009
-lots of CH4 escaping from
melting gas hydrates
-powerful positive feedback
on global warming
-CH4 is a powerful greenhouse gas
-most likely oxidizes to CO2 before
it enters the atmosphere… but still!
-see Archer et al., 2007 for
detailed investigation of
methane hydrate dissociation
during global warming
Westbrook et al., 2009
An interesting twist:
- replace CH4 with CO2 in the hydrate lattice
- have your energy cake and eat it too?
Park et al., PNAS, 2006
Take-home point
Methane hydrates represent the largest fossil fuel reservoir,
but problems ranging from yet-to-be-developed
technologies and climate change feedbacks remain to be
resolved.